1. Field of the Invention
The present invention relates to aromatic polyamide-imide polymers containing the hexafluoroisopropylidine or a 1-phenyl-2,2,2-trifluoroethane linking group having improved physical and chemical properties, and to a method for preparing such polymers.
2. Description of Related Art
Polyamide-imide polymers and copolymers are known in the art. These materials are generally prepared by the condensation polymerization of trifunctional acid monomers such as the 4-acid chloride of trimellitic anhydride (4-TMAC) and one or more aromatic diamines. Examples of such polyamide-imide polymers are disclosed in U.S. Pat. Nos. 3,347,828, 3,494,890, 3,661,832, 3,920,612 and 4,713,438.
These polymers may be characterized by extremely good high temperature properties (Tg of about 275.degree. C. or higher), good high temperature stability, good tensile strength at high temperatures, good mechanical properties and good chemical resistance. These polyamide-imides are useful as wire enamel coatings, laminates, molded products, films, fibers, impregnating varnishes and in other applications where high thermal stability is required.
One of the problems associated with such polymers is that they exhibit generally poor flow properties which render them difficult to process, particularly to injection mold or to spin into fibers. These polymers are also relatively hydrophilic and tend to absorb moisture which can effect their clarity, heat stability, processability, mechanical and electrical properties.
Applicants' copending U.S. patent application Ser. No. 07/316,380, filed in the USPTO on Feb. 27, 1989 now U.S. Pat. No. 4,954,610 polyamide-imide polymers prepared by forming the polymer condensation product of 4-TMAC and one or more diaryl diamines containing a tri or hexafluoroisopropylidene group linking the two aromatic moieties. Such polyamide-imide polymers exhibit enhanced solvent solubility and thermal stability and improved flow properties, as well as improved hydrophobic properties when compared with their counterparts which do not contain the tri or hexafluoroisopropylidene linking groups.